Over the last ten years, the materials most used for x-ray membrane applications have been boron nitride, silicon, silicon nitride, silicon carbide, and diamond. This work presents a review of the macroscopic properties (roughness, biaxial Young’s modulus, optical transmission, fracture strength, and radiation hardness) of these materials. From an examination of the overall criteria, it can be concluded that silicon carbide and diamond continue to be the potential material candidates, even if few properties of diamond membranes have still to be improved. On the other hand, to optimize the physical properties of the membrane material, one has to understand the relationship between the macroscopic characteristics of the membrane and its microstructure. To this aim, we have studied two types of SiC membrane materials, namely, (i) plasma enhanced chemical vapor deposited a-SiC:H and (ii) laser ablation deposited a-SiC. The microstructural characterizations were carried out by means of x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and elastic recoil detection analysis techniques. We were thus able to (i) point out the role of C-H and Si-H hydrogenated bonds and Si-C bonds in the stress evolution, from compressive to tensile, (ii) demonstrate the linear dependence of the biaxial Young’s modulus upon the Si-C bond density and (iii) show the effect of dangling bonds on the optical transmission.